The present invention relates to a high-pressure phase cubic spinel-type silicon nitride and its preparation method.
Japanese Patent Laid-Open Publication No. 2001-199714 discloses a method for preparing a high-pressure phase spinel-type silicon nitride in the prior art. In the prior art method, first a mixture of low-pressure phase silicon nitride powder and metal powder are pressurized to form a molding. This molding is placed in a stainless steel container and immobilized in the stainless steel container using a cover with screws. This stainless steel container is embedded in a large, steel cylindrical housing, and this housing is used as a target. A projectile equipped with a metal flying plate on the front surface of a high-density polyethylene servo is provided. The projectile is accelerated with an explosive gun and made to collide with the target. The molding is compressed by the shock wave generated by collision with the projectile to obtain a high-pressure phase silicon nitride.
However, since the projectile collides with one side of the housing, impact pressure only acts from one side on the molding inside the housing. If a relatively large amount of samples (mixtures of low-pressure phase silicon nitride powder and metal powder) is used in the prior art method, it is difficult for adequate impact pressure to act on the molding, resulting in low compression efficiency of the molding. In addition, due to the low conversion rate from low-pressure phase silicon nitride to high-pressure phase silicon nitride, a large amount of low-pressure phase silicon nitride remains after the compression. Moreover, due to the large numbers of lattice defects and impurities, a high-pressure phase cubic spinel-type silicon nitride having a low degree of crystallinity ends up being obtained. In the prior art method, a high-pressure phase cubic spinel-type silicon nitride was not produced efficiently.